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Magnetic Mott criticality in a κ-type organic salt probed by NMR

Nature Physics volume 5, pages 880–884 (2009)Cite this article

Abstract

Near a Mott transition1, which can be tuned by controlling either the charge-carrier density (‘filling’) or the correlation strength (‘bandwidth’), lies fascinating emergent behaviour, such as unconventional superconductivity2,3, and the understanding of the underlying Mott criticality is a longstanding challenge. Recent studies have showed that the bandwidth-controlled Mott criticality (BCMC) involves critical fluctuations in charge4,5 and lattice6,7 degrees of freedom. Spin is another degree of freedom and its antiferromagnetic fluctuations are ubiquitous in strongly correlated electrons8,9. However, the magnetic aspects of BCMC are unexplored. Here, we report on the magnetic criticality brought about by BCMC. Through NMR investigations on a κ-type organic salt, we observe critical suppression of antiferromagnetic fluctuations accompanied by the critical enhancement of conductance. The two criticalities show the same exponent within experimental error. Site-to-site electron hopping introduces doubly occupied and empty sites, which extinguish stroboscopically the local spins, probably resulting in the identical criticality in charge and spin.

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Figure 1: Structure of κ-(BEDT-TTF)2Cu[N(CN)2]Cl and the bandwidth-controlled Mott transition.
Figure 2: Bandwidth-controlled discontinuous Mott transition seen from 13C-NMR.
Figure 3: Insulator–bad metal crossover seen from 13C-NMR.
Figure 4: Continuous Mott transition at the critical temperature seen from 13C-NMR and conductance.
Figure 5: NMR characteristics around the Mott critical end-point.

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Acknowledgements

We thank S. Watanabe, M. Imada, J. Fujioka and Y. Takahashi for fruitful discussion. This work was partially supported by Grant-in-Aids for Scientific Researches on the Priority Area (Grant No. 17071003) and on Innovative Area (Grant No. 20110002) from the MEXT, a Grant-in-Aid for Scientific Research (Grant Nos 20244055 and No. 20540346) from the JSPS and the Global COE Program: Global Center of Excellence for the Physical Sciences Frontier.

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  1. Fumitaka Kagawa

    Present address: Present address: Multiferroics Project, ERATO, Japan Science and Technology Agency (JST), c/o Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan,

Authors and Affiliations

  1. Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan

    Fumitaka Kagawa, Kazuya Miyagawa & Kazushi Kanoda

Authors
  1. Fumitaka Kagawa
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  2. Kazuya Miyagawa
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  3. Kazushi Kanoda
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Contributions

F.K., K.M. and K.K. designed the experiments. F.K. carried out the experiments and analysed the data. F.K. and K.K. interpreted the data. K.M. grew the single crystals for the study. F.K. wrote the paper with assistance from K.K. and K.M.

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Correspondence to Fumitaka Kagawa.

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Kagawa, F., Miyagawa, K. & Kanoda, K. Magnetic Mott criticality in a κ-type organic salt probed by NMR. Nature Phys 5, 880–884 (2009). https://doi.org/10.1038/nphys1428

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